As much as 1-2 watts at a power level most of us don't ride at, when comparing cog sizes that are at the literal extremes of what is possible on a FG bike (I've never seen a fixed cog bigger than 24T). So it's correct to say that the efficiency difference is down in the noise, for all practical purposes.


I do try to use the biggest chainring and cog combination I can for my gearing, though. Chain wear increases with the angle the chain is forced to bend under load, and I'm pretty sure I can feel the difference in chordal action between a 13T and a 16T.